<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<script src="https://cdn.staticfile.org/vue/3.0.5/vue.global.js"></script>
</head>
<body>
<div id="app">
  <p>{{ counter }}</p>
  <button @click="counter += 1">+1</button>
  <button @click="counter -= 1">-1</button>
</div>

<script>
const app = {
  data() {
    return {
      counter: 0
    }
  }
}

Vue.createApp(app).mount('#app')


</script>

</body>
</html>